We Blogged It!
Final ASPIRE Station
By this posting the ASPIRE team has likely finished its last science operation with the midnight deployment of the MOCNESS. In her weekly report, Chief Tish describes a week of hard work in challenging conditions that included the first impenetrable ice and equipment failure.
High winds and currents thwarted an attempt to sample surface seawater from the trace-metal-clean towed fish during the eastward transect across the polynya. They were headed toward the break in ice that had been seen in the MODIS ice image (Jan 4 blog).
The Slocum glider had been deployed to sample in the polynya as they proceeded to the moorings. But it too had its problems. The glider sent a distress signal indicating a water leak, so they had to retrieve it.
Tish writes: “During the glider recovery in rough seas, one zodiac was punctured during crane operations and the backup zodiac's engine failed in the water. The glider was eventually recovered from the backup zodiac as it was being towed alongside the ship. This maneuver required expert handling of the ship by the captain and crew, in extraordinary combination with highly talented MTs in the zodiac. After the glider's successful recovery, we were all a bit relieved to have a long transit to Pine Island Bay.”
Unfortunately, the next challenge was not as successfully met. Turns out that the break in the ice near the Thwaites Ice Tongue was not there when they arrived! They speculate that the lead had closed up during the high winds. After 24 hours of trying to gain access, they decided to turn back into the Amundsen polynya.
The change in course brought renewed optimism. Tish explains, “We must have left the gremlins in the Ice Tongue, because activities over the next few days went very, very well. Our 3-d drift station in the SE corner of the polynya (near our moored trap) proved to be quite different from the earlier drift station to the north in terms of plankton community structure and flux, giving us more information about the mechanisms behind the high productivity here. Experimental work with the phytoplankton assemblages revealed for the first time the importance of diatoms (relative to Phaeocystis). Krill were less abundant, but we found many different kinds of carnivorous zooplankton, including a thick layer of small jellyfish in the deep waters.”
A three day drift station gave them time for CTD sampling, experiments, and the repair and redeployment of the glider into the west end of the polynya. They also conducted a transect alongside the western side of the trough leading to the Dotson Ice shelf and a series of stations up and downstream of a large iceberg (>1 nm wide, 300 m deep).
During this time, they encountered the Korean icebreaker Aaron. Tish says that friendly greetings were exchanged and Captain Maghrabi spoke to their bridge about any information they might have regarding ice conditions leading to Pine Island Bay (their ship had a helicopter onboard). However, they were not able to help.
Following the completion of the drift station, they turned their sights east again to the “highly prized moorings in Pine Island Bay”. Tish continues, “The winds had relaxed and a new lead was visible by satellite. This time we tried even harder and longer than before, and got much farther east (to 108.6°W) to a point on the ASAR (radar) image that we thought might be a transition to easier ice. But, the reverse was true. The ice actually became more compressed and harder to penetrate. At that point, we agreed that it was unsafe to continue toward Pine Island Bay. BSR#3, #4, #5, and #6 will have to remain where they are, for now.”
With the glider retrieved and after a station in the marginal ice zone, they headed back to the pack ice for moorings BSR #12 and #13. Although satellite images showed heavy ice cover in their location, they proceeded, remembering their success with BSR#14 in similar conditions. Tish:” We made excellent time through the pack ice (thanks to good ice images and excellent piloting) and arrived at BSR#13 ahead of schedule. The release indicated that the mooring was not upright, however, and we were unable to see any parts of the mooring using sonar. After sending a release command, the mooring did not rise to the surface. Dragging was not possible given ice conditions. A new mooring was deployed slightly up-slope from the previous mooring location.”
“We then proceeded onto the shelf, along the trough, where, in spite of very heavy sea ice, we successfully recovered BSR#12. Another mooring was redeployed at the same location. After so much effort, we were very pleased to end mooring recovery operations on a positive note!”
This final day finds the team conducting the last MOCNESS deployment for the crab larvae team in the far NW corner of the polynya near where they first entered. The location they’re in was under heavy ice when they first arrived in the polynya, but is now open enough for the plankton tow. They’re interested in this area because they think it may be where warm deep waters enter the polynya, “potentially seeding the region with deep-dwelling zooplankton”, according to Tish. She continues, “With the good steerage of the Captain and his mates, along with careful monitoring of ice by the MTs, we have completed the mid-day tow and expect to complete the midnight tow later this evening.” The accompanying images are of the Aldahan Tracer Team sampling snow for iodine isotopes from the “manbasket” during this last station.
Tish concludes: “Overall, the week has been a great challenge, with big payoffs. I continue to be impressed by the dedication of this team. They met each challenge with great skill and strong hearts. I know we are soon heading home, but I won't soon forget the most extraordinary Team ASPIRE.”
At the completion of this midnight station, the NBP began to steam towards the Ross Sea, to arrive in McMurdo on the 16th. It’s hard to believe that the science operations are complete. Many, many thanks to Chief Tish for providing the concise details of the voyage that made it possible to “experience” the adventure, and to all who contributed their expertise and reflections.
To the science team and the crew of the NBP: Those of us who have followed you “virtually” share in your successes and are VERY proud of you!
To those of you "at home": Thank YOU for the love and support you give these amazing people that allows them to do their job so well!
Safe seas NBP!
PS: Check back for more updates and images this coming week! ☺
Question of the Day
- What are Polynyas and why are they important to study?
Polynyas, are recurring areas of seasonally open water surrounded by ice.
Energy and material transfer between the atmosphere, polar surface ocean, and the deep sea in polynas provide polar ecosystems with just the right ingredients needed for high productivity and intense biogeochemical recycling.
Polynyas may be the key to understanding the future of Polar Regions since their extent is expected to increase with anthropogenic warming.